This invention relates to a ball-equipped screw and nut mechanism for converting rotary motion into translative motion, and for performing the reverse conversion.
Mechanisms of this type are known wherein there is at least one channel for circulation of the balls, bounded by corresponding helical grooves in the screw and nut. Such mechanisms are widely used for all motion conversions of the type indicated, where high efficiency and silent and sure functioning are required.
The motion conversion mechanism, according to this invention, is adaptable to all of the applications mentioned, but is particularly advantageous for those in which the nut and the screw of the mechanism must be actuated by an alternating relatively helical motion of low axial amplitude. Several methods are known for these latter appliations, but have been found to be disadvantageous.
A first method was contemplated limiting the number of balls engaged in the circulation channel in such a way that, for an extreme position determined by the nut on the screw, an interval corresponding substantially to the axial travel of the nut would be present between the head of the train of balls and the opposite end of the ball circulation channel. This method was found to be unsuitable, however, because, toward the end of the course of the nut, the balls slide in the circulation channel, rather than rolling therein, thus causing the temporary disappearance of the previously mentioned advantages of the mechanism in question.
In order to lessen the disadvantages of this first method, use was made of a locked circulation of balls, of the type already known for such mechanisms, and which provide for substantial axial travel of the nut. The locked circulation of the balls can also be achieved by particular machining of the nut, and the addition to the latter of auxiliary elements for guiding the balls. The nuts thus adapted however do not have a structure for symmetrical rotation and thus create a lack of balance which is troublesome in case of rapid rotation. Moreover, some of these known nuts have an external shape which is not compatible with the requirements of the particular application for which the screw and nut mechanism is intended.